Method of annealing aluminum



1 Ivor W. Mills, Glenolden, Pa.,

United States Patent umce Patented Nov. 13, 1958 2,861,020 METHOD OF ANNEALING ALUMINUM assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application July 29, 1953 11 Claims. (Cl. 148-131) No Drawing.

Serial No.

This invention relates to the processing or fabrication 01 aluminum. More particularly, it concerns the prevention of staining of aluminum during the operation of annealing the metal.

In fabricating aluminum into the form of plates or sheets, the metal is conventionally subjected to a rolling operation wherein it is passed one or more times through a rolling mill to press it into the desired form. In this operation lubricating oil customarily is applied continuously to the rollers to reduce friction and minimize the energy expenditure. Usually the oil used for this purpose is of relatively low viscosity, for example, within the range of 35-300 S. U. S. at 100 F., although oils of higher viscosity are used in some cases. Most of the commercial aluminum rolling operations are carried out by utilizing a petroleum oil having a viscosity between 35 and 75 S. U. S. at 100 F. The aluminum plates or sheets which leave the rolling mill retain on their surface a thin film of the oil which has been applied as lubricant. I

During the rolling operation the aluminum tends to undergo what is referred to as work hardening; and it is customary thereafter to anneal the hardened aluminum by subjecting it to a temperature above 600 F. Work hardened aluminum will anneal satisfactorily at a temperature of, for example, 650 F., and it would be desirable to conduct the annealingstep at about this temperature level. However, it has been found that at such temperature staining of the aluminum will occur due to the presence of the surface film of hydrocarbonoil, and that the surface generally will be left in a discolored, unsightly condition. This is apparently due to formation from the oil of a thin varnish-like deposit which adheres strongly to the metal and which cannot be removed by wiping. Hence, in order to avoid such staining in commercial practice, the aluminum is customarily annealed at a temperature sufficiently high to burn off the varnish deposit, usually at about 800 F. The use of such higher temperature substantially increases the expense of the annealing operation.

The present invention is directed to the avoidance of the above described stain formation during annealing of the aluminum. According to the invention, lubrication during the rolling operation is effected by means of a hydrocarbon oil in which has been incorporated a minor amount of very finely divided adsorptive material such as silica, carbon black, adsorptive clay, or the like. Hence the oil film which remains on the aluminum when it is subjected to the annealing step contains a minor proportion of such adsorbent. I have discovered that the presence of adsorbent in the film prevents formation of the adherent tarnishing film otherwise experienced and, instead, causes a surface deposit-Which is loose and Which can readily be removed mechanically such as by wiping or brushing. When this deposit is wiped from the aluminum, the surface is found to have a bright, mirror-like appearance with little or no trace of stain.

Practice of the invention thus involves lubrication of employed in annealing.

'cating oil distillate derived from naphthenic base the roller surfaces with hydrocarbon oil containing a minor amount of finely divided adsorbent, subjecting the rolled aluminum to a rleatively low annealing temperature at which staining would normally occur in the absence of the adsorbent, for example, to a temperature within the range of 600-750 F., and thereafter wiping the aluminum to remove the loose adsorbent-containing deposit and obtain a clean, shiny surface.

The adsorbent can be selected from a wide variety of granular materials known to have adsorptive properties. Examples of suitable adsorbents are silica of either hydrophilic or hydrophobic form, carbon black, adsorptive clays such as fullers earth or Attapulgus clay, bauxite, alumina, magnesia and titania. Inexpensive materials of suitable adsorptive character can be obtained from used cracking catalysts which have been discarded from commercial cracking plants. It is customary practice in moving bed or fluidized cracking operations to pass the catalyst through an elutriation zone in order to remove fines formed by attrition; and such finesconstitute a suitable source within the refinery of adsorbent for practicing the present invention.

The adsorbent must be extremely finely divided so that it will not have-an abrasive action on the rollers, and preferably should be of colloidal or near-colloidal size. As an example, commercially available silica products particularly suitable for the present purpose generally have average particle sizes of the order of 0.01-0.05 micron. Carbon black within the same particle size range is also available commercially. Other materials, which are usually obtainable in larger size than desired for the present purpose, can be reduced to the desired size range by conventional grinding procedures.

The base oil to which the adsorbent is addedmay be any of the usual hydrocarbon oils used in lubricating roller mills. It usually will be preferable to employ an oil of viscosity within the range of 35-75 S. U. S. at F., although oils having viscosities as high as, or higher than, 300 may be used if desired. The amount of adsorbent which should be added will depend upon the particular type of adsorbent selected and upon its particle size, with the effectiveness generally increasing as the size decreases; and upon other factors such as the viscosity of the base stock oil and the temperature 7 In any event, the absorbent should be added to the oil in amount at least exceeding 0.5% by weight of the mixture and usually in excess of 1.0%. For example, colloidal silica in amount of 1.0 will cause a noticeable decrease in the degree of staining of the aluminum but, as a general rule, will not entirely eliminate the stain. Usually a 3% proportion of the colloidal silica will avoid stain formation practically completely, although in some instances it may be desirable to employ a still larger quantity. The desired antistaining effect almost always can be secured with less than 10% adsorbent by weight based on the adsorbent oil mixture.

By way of illustration of the invention, a series of comparative tests was made employing as base stock a lubricrude oil and having a viscosity of 55 S. U. S. at 100 F. In each test 0.8 cc. of lubricant was spread over the upper surface of a 4" x 4 piece of aluminum sheet of inch thickness and the aluminum was then heated in an oven at 650 F. for 30 minutes. The condition of the surface to which the lubricant had been applied was observed following this treatment.

With the base stock oil alone, the aluminum surface had a vari-colored tarnish which could not be removed by wiping vigorously with a cloth. When 2% of colloidal hydrophobic silica having an average particle size of added to the base stock, a brownabout 0.01 micron was so rptive properties. Thus,

ish deposit formed on the aluminum; and this deposit was easily removable by wiping the surface with a cloth thereby leaving a polished silvery surface.

The use in the base stock of 1% of a commercial hydrophilic silica having an average particle size of about 0.022 micron yielded a brownish deposit which was partially adherent, so that the surface after being wiped was not entirely free of stain. Increasing the amount of the last-mentioned hydrophilic silica to 3% resulted in 'a brownish deposit which was readily removable by wiping to yield a bright surface.

Attapulgus clay which had been ground to a fine size so that it passed through 325 mesh screen was used in amount of 4% by weight based on the clay-oil mixture. This resulted in a surface having a brownish deposit which deposit obtained when silica was used, and which also could be wiped off readily leaving a clean, shiny surface.

The use of 4% of a commercial carbon black having an average particle size of 0.024 micron resulted in a black surface deposit.

was clean and bright.

By way of comparison, similar tests were made with two finely divided materials having substantially no adwhen tale was used, the aluminum was found to havea rough, brown tarnish which adhered tightly to the surface. Similarly poor results were obtained by employing another non-adsorptive material which was a commercial amine derivative of bentonite.

I claim: 1 1. In the annealing of aluminum having a surface film of hydrocarbon lubricant thereon, the method of prepresence of a surface film of lubricant comprising hydrocarbon oil having incorporated therein 0.5-10% of colloidal solid adsorbent.

2. Method according to claim 1 wherein the annealing temperature is within the range of 600-750 F.

3. Method according to claim 1 wherein the adsorbent is colloidal adsorptive silica.

4. Method according to claim 1 wherein the adsorbent is colloidal carbon black.

5. Method according to claim 1 wherein the adsorbent is adsorptive clay.

6. Method according to claim 1 wherein the adsorbent is used cracking catalyst.

7. Nethod of processing aluminum which comprises subjecting the aluminum to a rolling operation while effecting lubrication by means of a hydrocarbon oil having incorporated therein 05-10% of colloidal solid adsorbent, subjecting the rolled aluminum carrying a surface film of the lubricant to an annealing operation at a temperature in the range of 600750 F., thereby forming an adsorbent-containing deposit on the surface of the alumi- N num, and then mechanically removing the deposit.

8. Method according to claim 7 wherein the adsorbent is colloidal adsorptive silica.

9. Method according to claim 7 wherein the adsorbent is colloidal carbon black.

10. Method according to claim 7 wherein the adsorbent 1s adsorptive clay.

11. Method according to claim 7 wherein the adsorbent is used cracking catalyst.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Chemical Engineers Handbook, by J. H. Perry, third edition, McGraw-Hill, 1950, pages 888, 914, and 915. 

1. IN THE ANNEALING OF ALUMINUM HAVING A SURFACE FILM OF HYDROCARBON LUBRICANT THEREON, THE METHOD OF PREVENTING STAINING OF THE ALUMINUM SURFACE WHICH COMPRISES SUBJECTING THE ALUMINUM TO AN ANNEALING TEMPERATURE IN THE PRESENCE OF A SURFACE FILM OF LUBRICANT COMPRISING HYDROCARBON OIL HAVING INCORPORATED THEREIN 0.5-10% OF COLLOIDAL SOLID ADSORBENT. 